1. Field of the invention
The present invention relates to a multi-layered printed circuit board (PCB) for efficient electrostatic discharge (ESD) protection, and more particularly to a multi-layered PCB of mobile communication terminals that may improve ESD protection of LCD through efficiently protecting LCD signal lines such as data lines and control lines from ESD.
2. Description of the Related Art
Recently, metallic decorations are widely used in mobile communication terminals, as design of mobile communication terminals has been emphasized. In mobile communication terminals market, dual folder type mobile communication terminals are mainly manufactured and sold.
However, the dual folder type mobile communication terminals have a problem in that sub-LCD and main-LCD are vulnerable to static electricity (i.e., ESD). The reason why the dual folder type mobile communication terminals are vulnerable to static electricity is because many data lines and control lines are connected with folder portion comparing with existing mobile communication terminals.
Then, a general layout of PCB in mobile communication terminals will be described with reference to FIG. 1 as follows.
FIG. 1 illustrates a general main board PCB in mobile communication terminals, especially, a layout of inner layers having LCD signal lines.
As illustrated in FIG. 1, the PCB is a multi-layered PCB having at least a third inner layer 11, a fourth inner layer 12 and a fifth inner layer 13. Data lines 14 and control lines 15 in connection with LCD are positioned on the third inner layer 11, the fourth inner layer 12 and the fifth inner layer 13.
At this time, the data lines and the control lines on the third inner layer 11 are not protected from ESD by GND region on a layer above the third inner layer 11. And, the data lines and the control lines on the fifth inner layer 13 are not protected from ESD by GND region on a layer below the fifth inner layer 13.
Thus, the data lines and the control lines on the third inner layer 11 and the fifth inner layer 13 are easily damaged by ESD.
In this connection, FIG. 2 illustrates voltages of LCD signal lines on inner layers at the time of applying ESD to the general main board PCB.
It can be known from FIG. 2 that voltages of the data lines on the inner layer are 2.8 volt at normal condition and the voltages are suddenly increased to 4 volt when ESD is applied to the inner layer. In other words, the voltages of the data lines on the inner layer are suddenly increased at degrees of 1.2 volt when ESD is applied.
The surge of 1.2 volt, illustrated in ‘A’ part of FIG. 2, is too big for the data lines on the inner layer to endure, so that data signals, transmitted through the data lines on the inner layer, are easily damaged.
As circuits in the mobile communication terminals are being complicated, it is necessary to arrange more data lines and control lines on PCB. Thus, more ESD protection elements for protecting the data lines and the control lines are needed, so that difficulties in designing and manufacturing PCB are increased.
Further, it becomes difficult to arrange lots of elements on PCB because data lines and control lines occupy wide area of the PCB, as the number of the data lines and control lines are increased. Further, it becomes difficult to maintain original design of mobile communication terminals and to design multi-layered PCBs.